The American Israel Public Affairs Committee (AIPAC) is expected to spend north of $20 million on a risky gambit that could end up weakening decades of bipartisan support for the country. Prime Minister Benjamin Netanyahu, meanwhile, has dispatched his top military and diplomatic brass to help convince Congress to tear up the international agreement.

“In the coming decade, the deal will reward Iran, the terrorist regime in Tehran, with hundreds of billions of dollars,” Netanyahu said in a TV address the day the deal was signed. “This cash bonanza will fuel Iran’s terrorism worldwide, its aggression in the region and its efforts to destroy Israel, which are ongoing.”

The Obama administration, meanwhile, hasn’t been shy about telegraphing to Netanyahu that he’s playing with fire.

“I fear that what could happen is that, if Congress were to overturn it, our friends in Israel could actually wind up being more isolated,” Secretary of State John Kerry said in remarks to the Council of Foreign Relations in New York on July 24. “And more blamed.”

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Congress gained the right to review the deal after passing bipartisan legislation in May. The bill, crafted by Senate Foreign Relations Chairman Bob Corker, R-Tenn., creates a 60-day review period and allows Congress to ban Obama from lifting statutory sanctions, potentially killing the deal — if it can assemble a veto-proof majority.

The debate is severely testing the half-century-old AIPAC and its historic ability to mobilize pro-Israel activists in both parties.

AIPAC also has a charitable arm, the American Israel Education Foundation. Founded in 1990, AIEF has funded 1,034 trips to Israel for lawmakers and their staff since 2000, according to an analysis by LegiStorm, at a cost of more than $10.7 million — more than any other sponsor.

AIPAC isn’t a political action committee and doesn’t directly fund any electoral campaigns. A bevy of pro-Israel groups, however, spent more than $10.8 million on congressional candidates in 2012-14, according to an analysis by the nonprofit MapLight.

The lobby isn’t funded by the Israeli government, but its ties to Israel have come under scrutiny in the past. It was founded in 1951 as the American Zionist Committee by Isaiah L. "Si" Kenen, the former information director for Israel’s United Nations mission; it changed its name in 1959 and was incorporated in 1963.

Two of AIPAC's top officials were indicted in 2005 for passing secrets on to Israel, and critics routinely assert it is a de facto agent of the Israeli government — and, increasingly, the conservative Likud Party.

Israel itself currently employs the law firms Arnold and Porter and Sidley Austin, both of which provide legal advice on taxation and other matters but don’t lobby the US government or Congress. Israel shelled out almost $2.5 million for their services last year.

Despite the prime minister’s assurances that he’s just doing what’s best for Israel, the bitter debate can only further poison his already dismal relationship with the US president. Netanyahu himself injected more partisanship into the discussion when he accepted an invitation from House Speaker John Boehner, R-Ohio, to speak before Congress just before parliamentary elections in March.

The rancor has bled into other aspects of the relationship.

After Netanyahu dismissed any chance of Middle East peace during the election, the White House threatened to reassess its veto of pro-Palestinian resolutions at the United Nations. The change of tune came after Obama’s ambassador to the United Nations, Samantha Power, helped nix the Palestinians’ statehood bid in December.

“Our ally, Israel, has indicated that they're not committed to that approach anymore,” Obama spokesman Josh Earnest told reporters in March. “And so if that's the case, it means that we need to sort of rethink what our approach is going to be in the United Nations and other areas where we confront this question about how to resolve the differences between the Israeli people and the Palestinian people.”

And the State Department forcefully restated its opposition to settlement expansion after Congress passed legislation equating Israel with the occupied parts of the West Bank. The trade legislation provision calls on the United States to discourage the European Union from boycotting “Israel or persons doing business in Israel or Israeli-controlled territories” during free trade negotiations.

Support for Israel’s security, however, remains strong in both Congress and the administration.

The State Department’s foreign aid request for next fiscal year again seeks $3.1 million in military assistance, and Obama has offered even more as a consolation prize for the nuclear deal with Iran. Already, the president in March released aid to Egypt, once again a key Israel ally against Hamas under President Abdel Fattah al-Sisi.

Congress will also continue to have Israel’s back, no matter how it ends up voting on the Iran deal.

In May, the House passed an annual defense bill that calls for the joint creation of an “anti-tunneling defense system” to “detect, map, and neutralize” the underground tunnels militants have used to attack Israel. The provision from Reps. Gwen Graham, D-Fla., and Doug Lamborn, R-Col., is modeled after the wildly successful Iron Dome anti-missile program but doesn’t specify a funding amount.